Yarn inspection apparatus



Sept. 29, 1970 L. c. NICKEL-L ETAL 3,530,690

YARN INSPECTION APPARATUS Filed March 29, 1968 INVENTORS 6 Sheets- Sheet 1 Awzeuce Caemu Nucxeu, AYMOND Blames FERTIG HENRY T- Sessuous ATTORNEYS Sept. 29., 1970 L. C. NICKELL ET AL YARN INSPECTION APPARATUS 6 Sheota-Sheet 2 Filed. March 29, 1968 m w 0 8 m m M m 5 m m m u w. v MQ T mF w ss, meg, m n. 4H CAS w wtmm N N uwwm W 1333*, 5 a 2 L R H Y m k W m s I m fl 4 7-, 1. T m L 7 w A1 L L. C. NiCKELL ETAL YARN INSPECTION APPARATUS Sept. 29, 1970 e Sheets-Sheet 5 Filed March 29, 1968 a i s mu? m w R BK e0 M e Mn Me A r- N u o was w ENSPO w E\. 2% me 3 mmmiw me o lw A E J @IIITWQ Sept. 29, 1970 1.. c. NIC KELL ET AL 3,530,690

YARN INSPECTION APPARATUS Filed March 29, 1968 6 Sheets-Sheet 4 un mu+ United States Patent 015cc 3530 ,690 Patented Sept. 29, 1970 3,530,690 YARN INSPECTION APPARATUS Lawrence Creigh Nickel], Raymond Baines Fertig, and Henry T. Sessions, Ronceverte, W. Va., assignors to Appalachian Electronic Instruments, Inc., Ronceverte, W. Va., a corporation of West Virginia Filed Mar. 29, 1968, Ser. No. 717,076 Int. Cl. D04b 35/10 U.S. Cl. 66-163 14 Claims ABSTRACT OF THE DISCLOSURE Yarn inspection apparatus for detecting broken yarns in a yarn sheet of parallel yarns moving along a feed plane over at least a portion of its feed path, including a detector head adjacent one edge of the yarn sheet for projecting a narrow cross section light beam transversely spanning the width of the yarn sheet along a beam axis located closely adjacent but spaced to one side of the feed plane, a retro-reflective target adjacent the other edge of the yarn sheet for returning light to the detector head along the ray path of incident light projected by the detector head, and an air discharge tube paralleling the light beam and spaced to the opposite side of the yarn sheet to blow any broken yarns from the yarn sheet into the light beam.

BACKGROUND AND OBJECTS OF THE INVENTION The present invention relates to yarn inspection apparatus for continuously monitoring a large group of yarns arranged to move substantially in unison in side-by-side relation in the form of a warp or warps in one or more feed planes, the groups of yarns in each plane being hereinafter referred to as a yarn sheet, and detecting occurrence of any broken yarn ends in the yarn sheet for producing a defect signal.

Feeding of yarns in large groups as yarn sheets occurs in many different types of yarn handling apparatus, such as knitting machines, particularly of the tricot or warp knitting machine type, in weaving machines, in feeding of yarns from a warping machine to the beam or beams of knitting machines, and similar yarn making and textile manufacturing installations. When breakage occurs in any of the yarns making up such a yarn sheet, the sudden release of tension on the yarn, its twist characteristics, and the condition of the yarns in such yarn sheets cause the broken yarn end to engage and become entangled with or cling or adhere to an adjacent yarn rather than the broken yarn end falling freely out of the plane of the unbroken yarns. Immediate detection of any broken yarn end is essential for a number of reasons, as to avoid costly waste from production of defective fabric by the knitting machine into which the yarns are being fed, and to avoid rapid multiplication of yarn breakage as broken yarns cling to adjoining yarns and exert stresses thereon, which would increase the time required to correct the breakage situation and place the knitting machine back in service. Mechanical stop motions such as have been heretofore used in some types of textile machines having a relatively small number of yarns in each warp are not readily suitable for other types of textile machines, such as tricot knitting machines and the like devices having several thousand yarns in each yarn sheet, because of the lack of suificient space for the yarn sensing elements of such mechanical stop motions and because their effective use usually requires the released portion of the broken yarn to normally move freely beyond the plane of the yarn sheet.

Heretofore, it has been proposed to provide such textile knitting machines with photoelectric broken end detectors, wherein a light beam is directed transversely across the width of the yarn sheet and is spaced slightly to one side of the plane of the yarn sheet, in association with some type of pressurized air tube located adjacent the opposite side of the yarn sheet directing air currents therethrough in a direction to propel any broken yarn ends through the light beam so as to vary the intensity thereof and produce an output signal from the photocell indicating detection of the broken yarn. Such systems, however, have been subject to considerable problems, due to the long light path involved, the considerable vibration present in such textile machines and the difiiculty of making such optical detection systems compatible with this vibration, the difficulty of detecting very fine denier yarn as now frequently used in such textile machines over the long light paths involved, the vulnerability of such systerns to respond to spurious signals, because of their sensitivity to electrical surges from starting and stopping of other machines, line voltage fluctuations, and the presence of particles of dust and lint in the region of the detecting system. Also, it is difficult to find appropriate places to locate both the sizable light transmitting and light receiving units of such systems in the limited space available in knitting machines, as the machine parts frequently restrict severely the space where the yarn can be monitored. Additionally, the difiiculties of alignment and preservation of alignment of such devices, and the high skills required for realignment of such systems when they get out of adjustment, have all posed serious practical problems in attempted commercial use of such optical broken yarn detectors. Examples of prior patents disclosing this type of optical broken yarn detector systems are found in U.S. Pat No. 2,438,365 to Hepp, and No. 2,711,093 to Edelman et al.

An object of the present invention is the provision of novel yarn inspection apparatus for monitoring yarn sheets by providing a light beam spanning the width of the yarn sheet immediately adjacent but spaced out of the plane thereof and producing a defect signal upon passage of a broken yarn and through the light beam, which achieves reliable monitoring of fine yarn in yarn sheets of large width, which minimizes vibration and alignment problems, and which is more readily adaptable to be fitted into the limited spaces available in yarn handling machines.

Another object of the present invention is the provision of a novel broken yarn detection apparatus for moni toring yarn sheets of large width, wherein a monitoring light beam spans the width of the yarn sheet and is spaced slightly out of the plane thereof, and wherein the light for said light beam is projected from a detector head adjacent one edge of the yarn sheet and is returned to the detector head by a retro-reflective target located adjacent the other edge of the yarn sheet, or at a selected intermediate point between the edges thereof, to reduce alignment and vibration problems, increase sensitivity of the system, and facilitate detection of very fine yarns.

Another object of the present invention is the provision of novel detector head structure for a broken end detector as described in the immediately preceding paragraph.

Another object of the present invention is the provision of novel broken yarn end detector apparatus for monitoring a yarn sheet, wherein a light beam spans the width of the yarn sheet at a location spaced slightly out of the plane thereof adjacent one side of the yarn sheet, and pressurized air tube means span the width of the yarn sheet adjacent the opposite side thereof for blowing broken yarn ends into or through the light beam, wherein reduced power is required for a motorized blower supplying air to the tube to achieve effective air distribu tion in useful directions therefrom.

Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a fragmentary, somewhat diagrammatic perspective view, illustrating a typical installation of a broken yarn detecting apparatus of the present invention in conjunction with a two-bar, double width tricot knitting machine;

FIG. 2 is a somewhat diagrammatic, fragmentary, vertical section view illustrating a typical installation of the broken yarn detecting apparatus of the present invention incorporated in a three-bar tricot knitting machine;

FIG. 3 is a fragmentary perspective view illustrating a typical installation of the broken yarn detecting apparatus of the present invention, associated with a yarn sheet in the feed path between a creel of a warper and a beam and extending in a generally horizontal plane;

FIG. 4 is a rear elevation view of the detector hea employed in the broken yarn detecting apparatus of the present invention;

FIG'. 5 is a vertical longitudinal section view through the detector head, taken along the line 55 of FIG. 4;

FIG. 6 is an elevation view of the light mask associated with the lens barrel mount of the detector head, as viewed along the line 6-6 of FIG. 5;

FIG. 7 is a diagrammatic view of a typical air supply system for supplying pressurized air from a blower to the air discharge tubes of the broken yarn detector apparatus for a double width tricot knitting machine installation;

FIG. 8 is an exploded perspective view of the target structure employed with the broken yarn detector apparatus;

FIG. 9 is a schematic diagram of the preamplifier employed in the detector head;

FIG. 10 is a schematic diagram of a relay driver amplifier circuit which may be used with the broken yarn detector apparatus of the present invention;

FIG. 11 is a schematic diagram illustrating additional circuitry which may be associated with the relay driver amplifier circuit portions of FIG. 10, having plural input channels respectively associated with different yarn sheets in a tricot knitting machine installation to facilitate identification of the yarn sheet in which a broken end occurs;

FIG. 12 is a schematic diagram of a reset timing circuit usable with the broken yarn detecting apparatus of the present invention when the same is associated with a knitting machine to permit the operator to control the detecting apparatus automatically from the controls on the knitting machine, and

FIG. 13 is a schematic diagram of a regulated power supply which may be used with the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Referring to the drawings, wherein like reference characters designate corresponding parts throughout the several figures, and particularly to FIG. 1 diagrammatically illustrating the broken yarn detecting apparatus of the present invention in a double-width tricot knitting machine installation, there is shown the usual top warp beam 16 and bottom warp beam 17 of a conventional tricot knitting machine from which the yarns are fed under tension in yarn sheets 18 and 19 through the conventional reeds, indicated schematically at 20a and 20b, and tension bars 21a and 21b, to the needle position 22, where the yarns are knitted to form the knitted cloth product 23. The knitting machine of FIG. 1 is, for example, a double width machine providing a yarn sheet of approximately 168 inches or more width, although it will be appreciated that the installation will be similar for single width knitting machines having the usual yarn sheet width of about 84 inches. Disposed in the zone between the tension bars 21:: and 21b and the needle zone 22, and to the rear of the rearmost yarn sheet 19 fed from the lower beam 17, as viewed in FIG. 1, are a pair of air discharge tubes 24, 24a disposed in axial alignment so as to substantially span the width of the yarn sheets, each of the air tubes having an elongated air discharge slit 25, 25a extending substantially the length thereof and facing generally toward the yarn sheets. The two air discharge tubes 24, 24a, as is more clearly illustrated in FIG. 7, described in detail hereinafter, are supplied with pressurized air through suitable tubing, generally indicated at 26, from a conventional motor driven blower 27. If only a single width knitting machine is to be monitored, only a single air discharge tube 24 need be provided.

On the opposite side of the yarn sheets 18, 19, relative to the location of the air discharge tube 24, or tubes 24, 24a, and disposed slightly upstream therefrom relative to the direction of travel of the yarn, one or more detector beam assemblies are arranged to detect any broken yarn ends propelled from the planes of the yarn sheets 18, 19 in the direction of the detector beam assemblies by the air discharged from the tube or tubes 24, 24a. While certain installations need only one of such detector beam assemblies, as will be described later, three of such assemblies are illustrated in FIG. 1, designated respectively 28a, 28b and 28c. Each of the assemblies 28a, 28b and 280 are identical in construction and detailed description of one will suffice for each. The assembly 28a comprises a detector head 29 shock mounted outwardly of one edge, the proximal edge as viewed in FIG. 1, of the yarn sheet 18, for directing a high intensity light beam 30 of narrow cross section along a rectilinear axis so as to span the width of the yarn sheet 18 and be spaced slightly from the plane of the yarn sheet 18 to the side thereof opposite the side on which the tubes 24, 24a are located. Adjacent, and spaced slightly outwardly from, the opposite edge of the yarn sheet 18 is a rigidly mounted target assembly 31, formed of retro-reflective material, such for example as retrorefiective tape manufactured under the trade name, Scotchlite, by Minnesota Mining and Manufacturing Company, having the property of returning light along the same path as the incident light rays, regardless of the angle of incidence. The retroreflective target assembly 31 returns the light rays projected thereto from the detector head 29 back along the same light beam axis to the detector head 29, where the returning light rays are directed to a phototransistor, as hereinafter described, which responds to the intensity of light returned thereto. The components of the second and third detector beam assemblies 28b and 280 are identical to those of the assembly 28a and the components thereof are therefore indicated by the same reference characters used for the components of the assembly 28a. Signals derived from the phototransistors of the detector heads 29 are preamplified in the detector heads, and coupled to a relay driver amplifier unit 32 to activate the relay of a relay unit 33, and visual and/or audible alarms, if desired, to signal detection of a broken yarn end upon passage of a broken yarn end through either of the beams 30 and variation of the phototransistor current in response thereto.

The components in FIG. 2, illustrating a three-bar tricot knitting machine, which correspond to components of FIG. 1, are indicated by like reference characters, and a third or intermediate warp beam 17 is also illustrated, from which the yarns forming the middle yarn sheet 19 are drawn through a reed 20c and over a tension bar 21c and fed to the needle zone 22. It will be apparent from an inspection of FIG. 2 that, since the yarn sheets, whether there be two or three yarn sheets, are in almost vertical planes near the needles 22 and the air discharge tube 24 and detector beam 30 are adjacent the yarn sheets in this region, it is much easier to blow out a broken end from the plane of the yarn sheet through the detector beam 30. Especially in the case of the front yarn sheet 18, the broken end will swing out with very little air blowing on it, and in fact, since it is usually tilted downwardly and rearwardly from the tension bar 21a, the broken end from the front yarn sheet 18 will usually fall out without air. By locating the air discharge tubes and detector beam assemblies in this manner, a blower of quite low horsepower is adequate to insure blowing of broken ends into the light beam.

If the air idscharge tubes and detector beams were mounted adjacent the yarn sheets in the region near the beams 16, 17, between the reeds and the beams, difficulties are sometimes encountered in effecting reliable movement of the broken end into the path of the detecting beam. Particularly if the yarn breakage occurs between the reed and the needles, air will not always pull the broken yarn back through the reed from the needles, particularly with extremely fine yarns such as denier yarn, even if very powerful blowers are used. Also, even if the broken yarn is drawn back through the reed and blown into the light beam, frequently considerable time lag occurs before the light beam is altered by the broken yarn because of the drag involved, and a long flaw occurs in the cloth. With double width machines, particularly those using fine yarn such as 15 denier yarn for the rear yarn sheet 19, it is usually preferable to split the monitoring light beam for the rear yarn sheet, as illustrated in FIG. 1, using two detector heads 29, one On each side of the machine, and two of the target assemblies 31 arranged back-to-back in the middle of the machine. Because the target assemblies are extremely thin, generally planiform structures, space can be found for these in the middle of the machine, whereas the bulky light receiver structures of the former photoelectric detector systems could not be accommodated in such spaces. By splitting the rear detector beam 30, and routing the signals from their detector heads through separate channels assigned to each of the zones monitored thereby, it is much easier for the operator to find the broken end. However, it will be understood that a single detector beam assembly spanning the whole width of the machine can be used for the rear yarn sheet detector. If desired, and only one such detector beam assembly would be used for the rear sheet in single width machines.

While detector beam assemblies for each of the front yarn sheet and rear yarn sheet are illustrated in FIGS. 1

and 2, it will be apparent that, especially for the two-bar machine, it is possible to use only a single beam assembly 28a located to the front of the front yarn sheet 18, but disposed close thereto, as the air discharged from the tube 24 can blow the broken yarn forwardly from the rear yarn sheet 19 through the front yarn sheet 18 and into the light beam 30. With the three-bar machine, illustrated in FIG. 2, it is preferable to provide the detector beam assembly 28b between the middle yarn sheet 19 and the front yarn sheet 18 so as to be interrupted by broken yarn ends from either the middle yarn sheet 19 or the rear yarn sheet 19, while the front yarn sheet 18 is monitored by the second light beam assembly 28a.

An alternative installation for applications such as monitoring the yarn sheet being transported from a warping machine to the beam of a knitting machine is illustrated in FIG. 3, wherein the yarn sheet is indicated by the reference character 18. The detector beam assembly 28a, like that of the FIG. 1 and FIG. 2 installations, comprises a like detector head 29 directing a monitoring light beam 30 to the retro-reflective target 31 for return along the incident ray path to the detector head 29. The monitoring light beam 30 in this installation is spaced slightly above the plane of the yarn sheet 18' and an air discharge tube 24 similar to the correspondingly numbered air discharge tube of the FIG. 1 embodiment is spaced slightly below the yarn sheet plane and is supplied with pressurized air through tubing 26 from motorized blower 27. It will be appreciated that another practical broken yarn detecting installation could be provided by disposing the monitoring beam 30 slightly below the plane of the yarn sheet 18' and dispensing with the air discharge tube 24 and the pressurized air supply means associated therewith, as the broken yarn end would then fall by gravity through the monitoring beam 30 to interrupt or vary the intensity of the beam 30 and produce the desired defect signal.

Referring now to FIGS. 4, 5 and 6, the detector head 29 of the preferred embodiment herein illustrated comprises an outer casing 35 of generally box shape configuration having an apertured front end wall 35 which is provided with an opening 35a forming an optical aperture. A mounting block 36 is disposed within the casing and carried by the front end wall 35', to rigidly support in proper alignment the lamp 37, phototransistor 38, semi-transparent mirror 39 and a plano-concave lens 40. The lamp 37, for example, may be a General Electric Type 1876 having a short, fine filament and rather high light output, which draws about two amperes at 2.5 volts DC. This lamp is supported in appropriate bore in a portion of the mounting block 36, being retained therein, for example, by the set screw 36', to dispose the filament in alignment with a small aperture 41 at the rearmost end of the internal bore 41 in which the semi-transparent mirror 39 is mounted and with which the phototransistor 38 communicates through the bore extension 41a. Also mounted within the casing 35 is the preamplifier circuit 42 provided on a suitable printed circuit board or the like and fixed to the mounting block 36. Projecting externally from the front end wall 35 in concentric relation with the projected axis of the opening 35a is a lens tube mounting block 43 having an internally threaded aperture therein and a lens tube 44 having a constricted external threaded portion threaded into the bore of the mounting block 43 and carrying a plano convex lens 45 adjacent the outer end thereof. In the preferred example herein described, the planoconcave lens 40 has a 2-inch focal length and the planoconvex lens 45 has a 4-inch focal length.

The purpose of the small hole 41 in the mounting block 36 is to prevent light leakage caused by spurious reflections from reaching the phototransistor 38. This hole 41 and the filament of the lamp 37 are slightly displaced downwardly from the center axis of the two lenses 40, 45 to correct for the refraction occurring in the semi-transparent mirror 39. The light from the filament of the lamp 37 which passes through the small hole 41 is transmitted through the semi-transparent mirror 39 and is caused to diverge by the plano-concave lens 40. The virtual image of the filament produced by this lens 40 is about half the size of the filament, making it possible to project a narrow light beam over long distances. The divergent light from the plano-concave lens 40 then passes through the planoconvex lens 45, which is adjusted to a position to substantially collimate the light or produce a sharply focused image of the filament on the target 31. The reflected light from the target 31 travels back through the two lenses 45, 40 to the semi-transparent mirror 39, where it is reflected through a substantially angle into the bore extension 41a to the photo sensitive surface of the phototransistor 38.

The above arrangement provides a monitoring light beam of very narrow cross section appropriate for detection of opaque objects having an area equal to as little as about one percent of the light beam, so as to span a yarn sheet width of at least about 180 inches and permit detection of small yarns, for example, about 15 denier yarn, which has a diameter of about .003 inch. For monitoring light beams of inches or shorter, a three inch focal length plano-convex lens 45 may be used and adjusted for a slightly out-of-focus image, in the direction of collimation, on the target 31, having about the same area as the face of the plano-convex lens 45, which in practice may be about one inch in diameter. This focusing method produces a light beam which is more uniformly sensitive than would result from sharpl focusing the image of the filament on the target 31, as a sharply focused image of the filament would make the light beam more sensitive away from the detector head, due to the smaller cross sectional area of the beam.

For certain applications where it is desired to get very close to the object being monitored, as in the case of the yarn sheets 18, 19 in the tricot knitting machine application, a rectangular mask, indicated by the reference character 46, can be placed between the lens tube mounting block 43 and the exterior face of the front end wall 35, with its center in registry with the center axis of the opening 35a, to cause a light beam of rectangular cross section to be projected. This provides a larger signal than a circular cross section light beam in certain cases and is especially helpful where there is only a limited movement of the piece of broken yarn which may not drop through the light beam, but only becomes slack and barely enters the light beam. It is sometimes desirable for physical reasons to keep the light beam small, especially when the broken yarn detecting system is to be installed in a machine which has a limited clear light path and which may be vibrating. Of course, if any part of a vibrating machine enters the light beam, a false signal will result, rendering the device useless. The rectangular cross section mask 46 and a long focal length planocurvex lens makes an installation practical when such limiting factors are present. When a rectangular light beam is used, it is sometimes possible to mount the detector head at an angle which will permit a larger length or area of the object being detected to pass into the light beam and thus produce a larger signal.

Where light beams spanning distances up to about 200 inches in length are required, the four inch focal length piano-convex lens 45 is used, and is adjusted to produce a light pattern at the target 31 having an area of about the same size as the face of the lens 45, which is about one inch in diameter, with the image of the filament sharply focused and slightly larger in area than the face of the lens 45. Although this beam, producing the sharply focused image, is not absolutely uniformly sensitive along its length, satisfactory results are obtainable. If more uniform response along the length of the beam is desired, the plano-convex lens 45 may be changed to a five inch focal length lens, which requires a larger detector head, or the four inch focal length lens 45 can be retained and the lano-concave lens 40 changed to a one inch focal length lens. Either of these alternative solutions, however, result in slightly less light being projected, with decreases in the sensitivity of the system.

It will be appreciated that by locating the mask 46 between the lens tube mounting block 43 and the front end wall 35 of the outer casing, the mask does not move as it would if it were attached to the outer portion of the lens tube 44 in the vicinity of the lens 45, and thus the lens tube 44 can be freely adjusted through any small angle desired to achieve proper focusing or defocusing of the image. If the mask 46 were carried on the lens tube 44, the lens tube would have to be turned in 180 increments in order to maintain the mask properly positioned in relation to the projected image of the lamp filament, and such increments would not always produce optimum focusing conditions.

It is also to be noted that the plano-concave lens 40 2-inch focal length is mounted so that the fiat surface faces the semi-transparent mirror 39 and lamp 37. By arranging the lens 40 in this manner, light reflections from the curved surface of the lens are decreased. If the 2-inch focal length plano-concave lens 40 were arranged with the concave surface facing the semi-transparent mirror 39, it was found that this curved surface was apparently acting as a concave mirror to some extent, causing substantial light reflections to be returned to the phototransistor 38, causing a higher background current. By reversing the arrangement of the lens 40, the normally occurring reflections from the lamp to the phototransistor were greatly reduced so that practically all of the phototransistor current is a result of the light reflected back from the target 31, permitting a higher value of load resistor to be used before saturation occurs and increasing the sensitivity of the detector head. If the focal length of the lens 40 differs substantially from the light path distance between lens 40 and the phototransistor 38, it is sometimes advantageous to reverse the disposition of lens 40, disposing its flat surface towards the mirror 39.

As illustrated in FIGS. 4 and 5, the detector head casing 35 has a pair of axially aligned trunnions 47 projecting from the opposite sides thereof and received in apertures of corresponding cross section in a pair of upwardly projecting arms 48a of a mounting yoke 48. Set screws 48a are provided in the yoke arms to lock the trunnions 47 against rotation about the axes of the trunnions. Similarly, the base 48b of the yoke 48 is centrally apertured to receive a cylindrical post 4911 rising from a rubber shock mount assembly 49. The shock mount assembly 49 comprises a rigid top plate 49b and a rigid bottom plate 490, assembled together in spaced relation by bolts 49d at the four corners thereof extending through four, corner located, rubber shock mounts 49d. Set screws 48b in the yoke base 48b are provided to lock the yoke against rotation about the post 49a. The shock mounts are provided to protect the filament of the lamp 37 from excessive vibration. While vibration is not nearly as critical in this apparatus as it would be with a photoelectric system having separate transmitters and receivers, because the light beam can move around to some degree on the retro-reflective target 31 Without serious effect, the provision of the shock mounts reduces movement of the lamp and thus movement of the light beam on the lens system to minimize noise problems which might otherwise Occur from such vibrations.

The target assembly 31 is of simple construction and comprises a rigid, substantially rectangular backing plate 51 having a rectangular sheet of retro-reflective tape or similar retro-reflective material 52 on the face thereof. The retro-reflective tape 52 is covered with a thin glass plate 53, sealed with a gasket 54 and assembled to the backing plate 51 with a frame 55, to prevent dirt, lint, grease and other foreign matter from collecting on the retro-reflective tape 52. All of such contaminants cut down on the intensity of the light reflected back from the target and thus decrease the sensitivity of the system. Grease is particularly detrimental and hard to remove from the exposed surface of retro-reflective tape. By covering the tape 52 with the glass 53, it is very easy to remove these contaminants, and further it is found that they have a much smaller effect on the reflective properties of the target when they are on the glass surface as compared being on the surface of the tape. The glass 53, which is preferably about A inch in thickness or thinner, produces only very little attenuation of the light, but because of its presence, the target assembly cannot be mounted precisely at to the optical axis of the beam projected from the detector head or a reflection from the surface of the glass plate will occur and strike the lens 45 of the detector head. In such a situation, any slight movement of the target or detector head would change the amount of light returning back to the head and generate a very high noise signal. To avoid this, the target assembly 31 is fixed at a small angle a few degrees in either the vertical or horizontal plane to the axis of the detector head lenses 45, 40, so that these reflections from the glass plate which would otherwise occur are not directed back to the detector head.

The detector head can be simply aligned, by loosening the set screws 4812' on the bottom swivel joint defined by the post 490, after which the detector head is turned until the light beam strikes the approximate center of the target 31 in a horizontal plane, and the bottom set screws 48b are tightened. The set screws 48a for the side swivel joint defined by the trunnions 47 are then loosened and the detector head turned about the axis of these trunnions until the light beam strikes the approximate center of the target in the vertical plane, after which the set screws 4841 are tightened. Such an alignment procedure which can be readily performed, is something which is well Within the capability of many persons in the mill who would not be competent to perform the exacting alignment procedures required for photoelectric systems involving separate projectors and receivers.

Referring now to FIG. 7, pressurized air from the blower 27 is preferably delivered to the air discharge tube 24, and the air discharge tube 24a, if a double width machine installation is involved, by feeding the pressurized air to a pair of spaced locations substantially half way between the longitudinal centerof each tube and the end thereof. This is accomplished by means of the hose sections 56a, 56b and 560, preferably formed of threeinch diameter hose, and a pair of two-inch hose sections 57a, 57b, leading from the three-inch hose sections to air inlets 57a, 57b at the tube 24, and like inlets at the tube 24a, if present, spaced for example 42 inches apart and located 21 inches from the adjacent end of a tube which is 84 inches long. The air discharge tube 24 in this example has a diameter of about one and one-half inches. By using this particular feed hose arrangement, very little pressure drop occurs in the connecting hoses to the air discharge tube and substantially equal pressures exist at both inlets 57a and 57b to the air discharge tube 24. If the pressurized air from the blower were merely supplied to one end of each of the air discharge tubes, it is found that the air tends to blow sideways out of the portion of the slit 25 therein lying near the inlet end of the air discharge tube, due to the high flow rate down the length of the tube. By feeding the tube at the inlets 57a, 57b, spaced at intermediate locations along the air discharge tube, this effect is mini mized, as the air exiting from that portion of the slit 25 lying directly opposite the inlet 57a, 57b is directed perpendicular to the slit. While a very slight amount of sidewise blowing from the slit occurs to each side of the inlet due to fiow down the pipe, this effect is greatly minimized by the illustrated arrangement, since the flow is split between the two inlets and maximum flow in the air tube is cut down by a factor of about four relative to the end air feed type of system. It will be appreciated that the tubes 24, 24a may be further subdivided. longitudinally, if desired, to be disposed closely adjacent the yarn sheets without interference with machine parts, and that the blower 27 can be located to one side of the machine and supply air to one end of the manifold hose section 56b, 560, if it is more convenient to do so.

Referring now to' the particular schematic circuits which may be employed for this system, FIG. 9 shows the schematic circuit for the preamplifier 42 enclosed in the detector head 29. The preamplifier includes an emitter follower stage, a Zener diode regulator and several filter circuits. A regulated voltage of 28 V. DC. is used to supply power to the preamplifier 42. Capacitor 42C2 is a tantalum unit which is used to bypass any noise signals, especially high frequency transients, coming in on the 28 V. DC. supply. Resistor 42-R1 sets the current for the zener diode 42-CR1 to the correct value. Zener diode 42CR1 sets the voltage for the phototransistors 42-Q1 and its load resistor 42-R2. Capacitor 42-C1 limits the high frequency response of the phototransistor 42-Q1 to further suppress transients. Resistor 42-R2 is the load resistor for the phototransistors 42- Q1. When light strikes the phototransistor 42-Q1, a certain amount of current flows through 42-Q1 and the load resistor 42-R2, depending on the light level. If the light level decreases due to an obstruction entering the light path, less current flows through 42-Q1 and 42-R2. This produces a negative pulse across 42R2. This pulse is applied to the base of transistor 42Q2, an emitter follower stage having a high input impedance. This causes less current to flow through 42Q2 and produces a negative pulse across resistor 42-R3 in the emitter of 42Q2. This pulse will be slightly less in amplitude than the pulse applied to the base of 42-Q2 due to the emitter follower connection of 42-Q2. Resistor 42-R4 and capacitor 42-C3 form a filter network to further attenuate any high frequency transients. Since the output impedance in 42-Q2 is very low, the output impedance of the preamplifier is on the order of 1000 ohms, due to 42R4 for signal frequencies, which is satisfactory for this application. Resistor 42-R2 is also the calibrating resistor for the detector head. The 10K value shown is only a typical value. Its actual value depends on the light level and the gain of the phototransistor.

The relay driver amplifier 32, which responds to the signal output from the preamplifier 42 of the detector head, is a high gain, narrow bandwidth amplifier having an extended low frequency response and limited high frequency response. It consists of an integrated circuit operational amplifier directly coupled to a differential amplifier, followed by a silicon controlled switch which in turn operates the control relay of relay unit 33, and is schematically illustrated in FIG. 10. The signal, a negative pulse from the detector head, is connected to potentiometer 32-R1, the sensitivity control, by means of a shielded cable. The negative pulse appearing on the slider of 32-R1 is coupled to the negative input of an 809CE operational amplifier 32-A by capacitor 32-C1 and resistor 32-R2. There is a feedback resistor 32-R5 from the output to the input of the amplifier 32-A. The feedback network, consisting of 32-R5 and 32-R2, determines the voltage gain of the amplifier, in this case about 75. A small capacitor 32C3 is connected across 32-R5 and serves to limit the high frequency response of the amplifier. A voltage divider consisting of resistor 32-R3 and 32-R4 is connected across the 28 V. DC power supply. The junction of 32R3 and 32-R4 is connected to plus input of the amplifier 32-A and sets the DC. input and output levels of the amplifier. The output signal of the amplifier 32-A, a positive pulse, is direct coupled to the base of transistor 32Q1, which in turn appears across the emitter resistor 32R6. The positive pulse across 32-R6 is coupled to the emitter of transistor 32-Q2 by resistor 32R7. A positive pulse at the emitter of 32-Q2 causes a positive pulse to appear across resistor 32-R8 in the collector of 32-Q2. Capacitor 32-C5 across 32-R8 serves to limit the high frequency response of this stage. Resistors 32R9 and 32-R10 across the 28 V. DC. supply provide proper bias for the base of 32Q2. The positive pulse appearing on the collector of 32-Q2 is coupled by capacitor 32-C6 to resistor 32-R11 and by resistor 32-R12 to the gate of the silicon controlled switch 32-Q3. Resistor 32R12 and capacitor 32-C8 form a filter to eliminate high frequency noise signals from 32Q3. Diode 32CR1 protects 32-Q3 from high negative pulses. Resistor 32-R13 and 32-R14 across the 28 V. DC. supply comprise a voltage divider for supplying fixed bias to 32-Q3 which lessens temperature effects of 32Q3. Relay REL which may be incorporated in relay unit .33, resistor 32-R15 and manual reset switch 32-SW1 are in the anode circuit of 32-Q3. When a positive pulse of about 1 /2 volts is applied to the gate of 32-Q3, it conducts and energizes relay REl through current limiting resistor 32-R15 and 32-SW1. It will continue to conduct until the 28 V. DC. supply voltage is interrupted -by 32-SW1. One set of contacts on REl is used to operate an indicator lamp 32-11, while the other set of contacts is available for external control or alarm purposes. The diode 32-CR2 is used to suppress the inductive voltage pulse which ap- 1 1 pears across relay RE1 when 32SW1 opens. Capacitor 32-C7 is a transient filter for 32Q3, while 32-C2 is a transient filter for the 28 v. D.C. supply. 32-C2 is a tantalum unit which is superior for high frequency use.

The low frequency response of this amplifier is quite low and is determined by capacitor 32C1 and 32-C6. The high frequency response is determined by capacitor 32-C3, 32-C5 and 32-C8 and is usually adequate. If faster response is needed for a particular application, it is only necessary to make these capacitors smaller.

This relay driver amplifier circuit, illustrated in FIG. 10, is adequate for single yarn sheet applications, such as the type illustrated in FIG. 3, or one wherein the single monitoring beam is disposed slghtly below the plane along which the warped threads are fed. However, in the double width tricot knitting machine application previously referred to, in the particular embodiment wherein a front detector beam assembly 28a spanning the full width of the front yarn sheet 18, and a pair of rear detector beam assemblies having their detector heads located outwardly of the opposite lateral edges of the rear yarn sheet and a pair of back-to-back target assemblies 31 in the center of the machine, a slightly modified relay driver amplifier circuit is desired wherein three separate amplifier channels lead from the three respective detector heads 29 and an indicator lamp is associated with each channel for respectively indicating the beam which detected a broken yarn end. Such a modification of the relay driver amplifier circuitry is illustrated in FIG. 11, with that portion to the left of the broken line 10', 10', corresponding to the schematic circuit illustrated to the left of the similarly numbered broken line in FIG. 10. It will be noted that in the circuit of FIG. 11, normally closed relay contacts 3E, SD of relay RES, to be later described, and resistors 32-R16 and 32-R15 are connected between the manual reset switch SW1 and the silicon controlled switch 32-Q3. When a signal fires 32-Q3, current flows through current limiting resistor 32-R16 and indicator lamp 32-11, which is used to identify the channel which detected the broken piece of yarn. Across 32-I1 is a resistor 32-R15' which parallels the lamp and allows the rest of the circuitry to work even if the lamp burns out. Each of the other two channels is identical to channel 1 and connects to the circuit of FIG. 11, as indicated. Connected to the cathode of 32-Q3 in channel 1 and also in channels 2 and 3 are diodes 32CR2, 32-CR3 and 32- CR4 for isolating the three amplifiers from each other. The current flowing through resistor 32-R13 causes the voltage on the anode of diode 32-CR2 to be sufiicient to pass additional current through resistor 32-R26 and the base of transistor 32-Q4 which causes it to conduct. Resistors 32-R26 and 32-R27 form a voltage divider to prevent 32Q4 from conducting because of the fixed bias, about 1 volt, on the cathode of 32Q3 before it fires. When 32-Q4 conducts, relay RE2 is energized through current limiting resistor 32-R17. One set of contacts on 32-RE2 turns on indicator lamp 32-I2 and the other set applies 28 v. D.C. to the RC timing network composed of 32-C9 and 32-R19. This produces a positive pulse across resistor 32-R19 which is applied to the gate of field elfect transistor 32-Q5, a very high input impedance device. This causes it to conduct. Initially, it was cut off by the voltage divider composed of resistors 32-R23 and 32-R22 from the 28 v. D.C. supply to ground, applying fixed bias to the source of 32-Q5. When current flows through resistor 32-R21, a negative voltage is applied to the base of PNP transistor 32-Q6, which causes it to conduct and energize relay REl through current limiting resistor 32-R24. One set of contacts on REl turns on indicator lamp 32-I3, while the other set energizes the stop relay RE7, the contacts of which are in the control circuit of the knitting machine and cause it to stop when the contacts open. Resistor 32R19 and diode 32-CR6 are used to discharge 32-C9 through resistor 32-R18. Resistor 32-R20 is current limiting resistor for 32-Q5.

The diode 32-CR7 across relay RE1 is used to suppress the inductive voltage from REI when 32-Q6 cuts off. The R-C network of 32-R25 and 32-C10 across relay RE7 is another inductor spike suppressor. The relay contacts RE3D and RESE in the anode circuit of 32-Q3 are automatic reset contacts for 32-Q3 which in turn resets relay RE2.

FIG. 12 shows a stop and reset timing circuit 60 to permit the operator to control the broken yarn detector automatically from the conventional controls on the knitting machine. In other words, the holding coil on the machine automatically resets the detector system. The reset timing circuit works as follows: When the operator closes the start switch on the knitting machine, relay RE6 is energized from the holding coil in the control circuit of the machine. This causes contact RE-6B and RE6C to close, charging 60C1 through 60-R3 from the 28 v. D.C. power supply. 60-R1, 60R2 and 60-CR1 form the discharge path for 60C1. The positive voltage pulse formed across 60R3 is applied to the gate of '60-Q1 by current limiting resistor 60R4. This causes 60Q1 to conduct, since the applied pulse is much higher than the fixed bias applied to the source of 60-Q1 by resistors 60R7 and 60R5. The negative voltage pulse across 60-R6 is applied to the base of PNP transistor 60Q2 and causes it to conduct through RE3 and 60R8. When RE3 is energized, it opens contacts RE3D and RE3E in the anode circuit of 32-Q3 (see FIG. 11) in the relay driver amplifier for about .8 second. It also resets the silicon controlled switches in the other amplifier channels at the same time. Relay contacts RE3B and RE3C causes indicator lamp 60I1 to light (to show the relay has closed for trouble shooting purposes) for the duration of the reset period.

FIG. 13 shows a power supply circuit 61 which may be used with the three detector beam installation, whereby two highly regulated feedback type power supplies provide 28 v. D.C. for the relay driver amplifier 32 and preamplifier 42 and 2.5 v. D.C. for the detector head lamp 37. In the 2.5 v. D.C. regulator the 7.5 v. A.C. winding of power transformer 61-T1 is rectified by bridge rectifier 61-CR1 and filtered by capacitor 61-C1. This voltage is applied to the collectors of transistors 61-Q4, 61-Q5, 61-Q11, 61-Q12, 61-Q13 and 61-Q14. It will be seen that there are three power transistors in parallel, 61-Q5, 61-Q12 and 61Q14, which are driven by the three driver transistors 61Q4, 61-Q11, 61-Q13, to provide an appropriate 2.5 v. D.C. supply to the three detector heads. The voltage at the junction of emitter resistors 61-R25, 61-R27 and 61-R29 is applied to the base of transistor 61-Q3, which is one-half of a differential amplifier, through resistor 61-R10. Across zener diode 61CR3 is a voltage divider composed of resistors 61R4, 61-R5 and 61-R6. 61-R5 is the voltage adjust potentiometer. The voltage on the slider of this potentiometer is the reference voltage. Any difference between the reference voltage and the output voltage is amplified by the differential amplifier composed of 61-Q2 and 61- Q3, which are matched transistors for low drift with temperature. The output of 61-Q2 is connected to the base of transistor 61-Q1. The collector of -61-Q1 is connected to the base of 61-Q4, 61Q11 and 61-Q13, which in turn drive the base of their companion power transistors. This completes the feedback loop, and because of the high loop gain used, insures good regulation.

To better understand the action of the regulator, assume a small positive voltage increase at the output of the regulator. This voltage is applied to the base of 61-Q3, which causes 61-Q3 to draw more current. This produces a positive voltage across the emitter resistor 61-R7, which is applied to the emitter of 61-Q2. This causes 61-Q2 to draw less current, which causes the collector of 61-Q2 to go positive. As the collector of 61-Q2 is connected to the base of 61-Q1, this positive voltage change causes 61-Q1 to draw less current, since 61-Q1 is a PNP transistor. When 61-Q1 draws less current, the

voltage across the emitter resistor 61-R2 goes negative. The collector of 61-Q1 is connected to the base of 61- Q4, 61-Q11 and 61-Q13, which causes them to draw less current. Since the emitter current of the driver transistors is the base current of the power transistors, this causes the latter to pass less current and bring the output voltage of the regulator back to 2.5 V. DC.

Capacitor 61-C2 is a small capacitor used to prevent high frequency oscillation of the regulator. Capacitor 61-C3 is used to further filter the output of the regulator. Resistor 61-R10 is used to cause the base of 61-Q3 to see about the same source resistance as 61-Q2 for balanced circuit operation. Diode 61CR2 is used to bias the emitter of 61-Q1. Resistor 61-R3 is the current setting resistor for zener reference diode 61CR3. It receives its voltage from the 28 V. DC. regulator.

The operation of the 28 V. DC. regulator is very similar to the operation of the 2.5 V. DC. regulator and thus need not be explained. The DC. stability of both regulators is excellent because of high quality reference type zener diodes and balanced differential amplifiers being used. This is important, because any change in the output of these regulators, especially the 2.5 V. DC. lam regulator, will change the sensitivity of the system due to a change in the light level. Changes in the output of either regulator will also cause noise problems, especially low frequency changes, because of the extended low frequency response of the relay driver amplifier.

For systems having only one detector head, it will be appreciated that the transistors 61-Q11 to 61-Q14 and their interconnecting circuits can be eliminated, leaving only the driver transistor 61-Q4 and the power transistor 61Q5 connected to the circuits of transistors 61-Q1, 61- Q2 and 61-Q3 and to the bridge rectifier 61-CR1 in the manner indicated.

While certain embodiments of the present invention have been particularly shown and described, it will be apparent that various modifications may be made therein within the spirit and scope of the invention, and it is desired therefore that only such limitations be placed thereon as are imposed by the prior art and set forth in the appended claims.

What is claimed is:

1. Yarn inspection apparatus for detecting broken yarns in a yarn sheet of plural substantially parallel yarns moving in a selected direction and lying in a feed plane, comprising a detector head located outwardly adjacent one edge of the yarn sheet having a light source and photodetector means therein and lens means for projecting light from said source in a narrow cross section monitor beam transversely spanning the yarn sheet and spaced in a direction perpendicular to said feed plane to one side thereof, retro-reflective target means located outwardly adjacent the opposite edgeof the yarn sheet having a sub stantially flat surface for retro-reflecting incident rays of said beam back along their incident ray paths to said detector head, semi-transparent mirror means for directing retro-reflected light entering said detector head onto said photodetector means, rectilinear elongated air discharge tube means supplied with pressurized air and having air discharge slot means facing said yarn sheet, said air discharge tube means paralleling said beam in substantially coextensive longitudinal relation thereto and being spaced from the opposite side of said yarn sheet to propel air toward the yarns and blow any broken yarn ends into said beam, and circuit means activated by variations of said photodetector means responsive to variations in light intensity sensed thereby for generating a defect signal upon interception by said beam of any broken yarns.

2. Yarn inspection apparatus as defined in claim 1, in combination with a tricot knitting machine having a warp beam and a yarn sheet fed therefrom through a read station and thence in a downward generally vertical direction to a needle station, said monitor beam and air discharge tube means being located substantially in a horizontal alignment on opposite sides of the generally vertical portion of the yarn sheet between said reed and needle stations with said air discharge tube means directing discharge air substantially horizontally through said yarn sheet.

3. Yarn inspection apparatus as defined in claim 2, wherein said knitting machine includes a plurality of yarn sheets extending downwardly along converging planes from said reed station to said needle station, said air discharge tube means and monitor beam having a pair of said yarn sheets disposed therebetween whereby the air discharged from said tube means blows any broken yarns from the yarn sheet nearest said tube means through the other yarn sheet of said pair and into said monitor beam.

4. Yarn inspection apparatus as defined in claim 1, wherein said yarn sheet extends along a feed plane section adjacent said monitor beam and air discharge tube means in a downwardly directed plane inclining toward said tube means whereby gravitational forces on said yarns cause any broken yarns in said feed plane section to move out of the plane of said section toward said monitor beam.

5. Yarn inspection apparatus as defined in claim 2, wherein said yarn sheet in the region between said reed and needle station extends along a feed plane section adjacent said monitor beam and air discharge tube means in a downwardly directed plane inclining toward said tube means whereby gravitational forces on said yarns cause any broken yarns in said feed plane section to move out of the plane of said section toward said monitor beam.

6. Yarn inspection apparatus as defined in claim 1, wherein said retro-reflective target means comprises a thin, substantially planiform target member including a sheet of retro-reflective material facing said detector head.

7. Yarn inspection apparatus as defined in claim 6, wherein said target means includes a transparent glass plate covering the surface of said retro-reflective material facing said detector head, said glass plate being located in a plane inclined at a slight angle away from prependicular relation to incident light rays from said detector head to minimize reflection of such rays from surfaces of said glass plate to the lens of said detector head.

8. Yarn inspection apparatus as defined in claim 2, wherein said target means comprises a thin, substantially planiform target member including a sheet of retro-reflective material facing said detector head and a transparent glass plate covering the surface of said retro-reflective material facing said detector head, said glass plate being located in a plane inclined at a slight angle away from perpendicular relation to incident light rays from said detector head to minimize reflection of such rays from surfaces of said glass plate to the lens of said detector head.

9. Yarn inspection apparatus as defined in claim 5, wherein said target means comprises a thin, substantially planiform target member including a sheet of retrorefiective material facing said detector head and a transparent glass plate covering the surface of said retroreflective material facing said detector head, said glass plate being located in a plane inclined at a slight angle away from perpendicular relation to incident light rays from said detector head to minimize reflection of such rays from surfaces of said glass plate to the lens of said detector head.

10. Yarn inspection apparatus as defined in claim 1, wherein said air discharge tube means include a motorized air blower having a pressurized air discharge, an elongated air discharge tube having said slot means extending substantially uninterruptedly along the length thereof, said tube spanning a selected portion of the yarn sheet adjacent the latter to propel air toward the yarns, and conduit means communicating said air discharge of the blower with plural locations along the length of said tube substantially symmetrically spaced relative to its longitudinal center and disposed substantially midway between the latter and the respective ends of said tube.

11. Yarn inspection apparatus as defiined in claim 2, wherein said air discharge tube means include a motorized air blower having a pressurized air discharge, an elongated air discharge tube having said slot means extending substantially uninterruptedly along the length thereof, said tube spanning a selected portion of the yarn sheet adjacent the latter to propel air toward the yarns, and conduit means communicating said air discharge of the blower with plural locations along the length of said tube substantially symmetrically spaced relative to its longitudinal center and disposed substantially midway between the latter and the respective ends of said tube.

12. Yarn inspection apparatus as defined in claim 9, wherein said air discharge tube means include a motorized air blower having a pressurized air discharge, an elongated air discharge tube having said slot means extending substantially uninterruptedly along the length thereof, said tube spanning a selected portion of the yarn sheet adjacent the latter to propel air toward the yarns, and conduit means communicating said air discharge of the blower with plural locations along the length of said tube substantially symmetrically spaced relative to its longitudinal center and disposed substantially midway between the latter and the respective ends of said tube.

13. Yarn inspection apparatus as defined in claim 1, including mounting means for said detector head comprising a yoke having upwardly extending arms and a lower cross member, said detector head including a casing having trunnion members projecting oppositely therefrom along an axis lying transversely of the axis of said monitor beam, said yoke arms having means for journaling said trunnions for angular adjustment about their axis and means for locking the same at angular positions to which they are adjusted, a shock mount for said yoke having a cylindrical post rising therefrom, and said cross member having means journaling the same on said post for angular adjustment of said yoke about an axis perpendicular to the trunnion axis and means for locking said yoke at positions to which it is adjusted.

14. Yarn inspection apparatus as defined in claim 1, wherein said lens means comprises a plane-concave lens disposed along a selected axis in alignment with said mirror and light source with its planar surface facing said mirror and light source, and a plane-convex lens spaced along said selected axis on the concave surface side of said piano-concave lens.

References Cited UNITED STATES PATENTS 2,346,240 4/1944 Thomas 250-219 XR 2,438,365 3/1948 Hepp et al. 66-163 2,464,468 3/1949 Thomas 66-163 2,570,381 10/1951 Roughsedge 250-219 XR 2,563,906 8/1951 Astill et al. 66-163 2,711,093 6/1955 Edelman et al 66-163 3,041,461 6/1962 Lindemann et al. 250--219 3,174,046 3/1965 Linemann et al. 250-219 3,379,225 4/1968 Ichimi et al. 139-353 3,401,267 9/1968 Engle et all 66-163 XR RONALD FELDBAUM, Primary Examiner U.S. Cl. X.R. 250-219 

